absorbed dose

absorption

a) A process in which the photon energy is captured by a medium, without transmission or reflection. (CS 7)
b) The process by which the molecules released from digested food pass through the wall of the gut and into the surrounding blood vessels. (CS 3)

acidosis

action potential

A sudden change in potential difference (voltage) across the cell membrane of neurons, consisting of an increase in the resting potential and a sudden return to the resting value. Transmitted along axons and constitute the principal 'language' of communication within nervous systems. (CS 2 & 3)

acute inflammation

acute pain

adaptive characteristic

A characteristic of an organism is said to be adaptive if an individual possessing that characteristic has an advantage over other members of the same species in terms of survival or reproduction; e.g. ability to evade predators, attractiveness to the opposite sex. (CS 1)

adaptive value

addiction

An excessive engagement in an activity despite negative consequences and a dependence upon the activity such that when access is denied, craving and withdrawal symptoms are seen. Most usually refers to dependency on a chemical substance but need not do so (e.g. gambling). (CS 3)

adhesion

affect

age-related macular degeneration

Degenerative disease of the retina that results in loss of vision in the centre of the visual field. It is caused by an impaired blood supply to the macula. This condition is usually associated with ageing. (CS 7)

age-standardisation

A mathematical adjustment that enables disease and mortality rates to be compared from countries with different age-structures, i.e. different proportions of young, middle-aged and older people in their populations. The method involves taking a very large 'reference population' (e.g. the whole of the world) and using its population age-structure as the 'standard' or reference point to which the different age-structures of individual countries are adjusted to remove the distorting effect. (CS 3, 4, 5 & 6)

agriculture

alcohol myopia

This term indicates alcohol's effect in inducing 'psychological short-sightedness'. Alcohol lowers the range of attention, so that immediate events take on more importance than their future consequences. (CS 3)

aqueous humour

arterial blood gas test

A test that measures the levels of oxygen and carbon dioxide in a sample of blood from an artery, e.g. in the wrist. Used to evaluate the efficiency of gas exchange between the blood and the lungs. (CS 5)

atmospheric pressure

atom

The smallest unit of an element that still has the properties of the element. Made up of a positively charged atomic nucleus, containing protons and neutrons, surrounded by negatively charged electrons. (CS 1, 2, 3, 4, 5, 6 & 7)

autobiographical memory

autograft

autonomic nervous system

That part of the nervous system which exerts an influence over a number of the internal organs of the body, such as the gut, heart and blood vessels. Functions without conscious intervention. (CS 2 & 5)

axon

The part of a neuron that consists of a long wire-like projection, ending in a terminal which participates in a synapse with another cell. Action potentials are transmitted along these. (CS 2, 3, 6 & 7)

blind study

blood pressure

The pressure exerted by blood pressing on the walls of the arteries. This is frequently expressed as two numbers, systolic (higher pressure during heart contraction) and diastolic (lower pressure between heart contractions), measured in mmHg. (CS 6)

blood-alcohol concentration

body mass index

A measure of body weight, taking height into account. Calculated by dividing person's weight (mass) in kilograms (kg) by their height in metres squared (m2). In most assessments, 20.0-24.9 is considered to be a normal healthy weight, 20.0 is categorised as underweight, 25.0 to 29.9 is said to be overweight, and greater than 30 is defined as clinically obese. (CS 1)

bone marrow

brain imaging

A technique for monitoring the activity of the different regions of the brain. One method involves injecting a radioactive tracer substance and measuring its later appearance in different brain regions; high concentrations correspond to regions of high activity in the neurons located there. (CS 2)

cardiovascular system

cartilage

Tissue that is found at joints and during bone repair. Its structure is a bit like bone without the mineral component, giving a smooth and resilient surface to the ends of bones to aid movement at joints. (CS 6)

cell membrane

cell

The basic structural unit of all organisms; there are many different kinds in multicellular organisms. In mammals, including humans, they are usually composed of a nucleus containing genetic material, surrounded by the watery cytosol containing various other organelles such as mitochondria. Enclosed by a membrane. (CS 2, 4, 5, 6 & 7)

cellular respiration

The process whereby oxygen is taken up by cells and used in chemical reactions involving the oxidation of nutrient molecules (e.g. glucose) derived from food; these reactions release usable chemical energy for cellular processes. (CS 5 & 7)

chemical compound

chemical formula

Tells you which type of atoms are bonded together to make up a compound or molecule, using symbols for its constituent elements. It also shows how many of each type of atom there are (e.g. the formula for carbon dioxide, CO2, shows it has one carbon and two oxygen atoms). (CS 3 & 5)

chemical symbol

Each element has been assigned one of these - often the first letter, or two of the first letters of the name; for example, H stands for hydrogen, C for carbon, N for nitrogen, Ca for calcium and O for oxygen. (CS 3 & 7)

choroid

chronic bronchitis

A condition characterised by inflammation of the walls of the airways and excess production of mucus. It results in a persistent (chronic) cough with production of sputum, obstruction of airflow and increased vulnerability to respiratory infections. (CS 5)

cirrhosis

classical conditioning

A form of conditioning in which a stimulus with no intrinsic capacity to trigger a particular response acquires such a capacity by being paired with a stimulus that does trigger the response; e.g. a bell can come to trigger salivation in a dog if it is repeatedly presented at the time food is given. (CS 2 & 3)

closed-angle glaucoma

cognition

Certain kinds of activity with which the brain is engaged, i.e. the processing of information that is summarised by the term 'mind'. It is exemplified by thinking, memory, reasoning and interpreting. (CS 2)

cognitive-behavioural therapy

A technique where people learn to change their thought patterns and behaviour to create feelings of coping and self-efficacy; e.g. people in chronic pain might be taught to place a less catastrophic interpretation on their pain. (CS 2)

complementary colours

concave

conditional stimulus

A stimulus that has no intrinsic power to trigger a particular response but which acquires this power after being associated with another stimulus. For example, a bell does not normally trigger salivation but, after pairing with food, it acquires this capacity. The capacity of the conditional stimulus is said to be conditional upon the association. (CS 3)

cones

confounding factor

Any factor which is statistically associated with a particular outcome (e.g. the incidence of a disease), but which is not involved in its causation. The association can disguise the true cause (or causes) of the outcome. (CS 3 & 6)

contagious

convex

cornea

The curved transparent layer that covers the front part of the eye. This (together with the lens) refracts light to form of an image on the retina, as well as protecting the eye from frontal damage. (CS 7)

dermis

deterministic

The effects of ionising radiation are said to be this if there is a threshold below which there is no effect, and if above that threshold, the severity depends on the amount of radiation received. (CS 4)

developed countries

Countries that provide universal education for their children, with populations that have high rates of literacy, comprehensive health services and which meet certain other development indicators, such as 100% access to safe drinking water and sanitation. Their economies grew rapidly in the early 20th century as a result of industrialisation, and they include all the richest nations on Earth (also known as 'high-income countries'). In some classifications, the countries of the former Soviet Union are included in this group; in others they are classed as 'transitional economies'. (CS 1, 2, 3, 4, 5, 6 & 7)

developing countries

Countries that are only partly industrialised and where national wealth is below that of the developed economies (also known as low- and middle-income countries). They rely to a much greater degree than developed countries on subsistence farming, small industrial businesses and low-paid unskilled or low-skilled labour. Major indicators of development, such as literacy and provision of clean water vary hugely between these countries. (CS 1, 2, 3, 4, 5, 6 & 7)

diastolic blood pressure

diffusion

The movement of atoms or molecules from a region of higher concentration to a region of lower concentration, until the concentration is the same throughout the available volume. Atoms and small molecules can also move across a permeable cell membrane by diffusion, if a concentration gradient exists (e.g. between the inside and the outside of the cell). (CS 3, 5, 6 & 7)

disability adjusted life year

A measure of the real impact of a particular disease, disorder or disability on people's lives (DALY), combining an estimate of the number of years lived with a reduced quality of life, taking into account the severity of the condition (every condition is assigned a 'weighting factor' to reflect this), and the number of years of life lost if the person dies prematurely, based on their age and the average life expectancy in that population. (CS 1, 3, 5 & 6)

disease risk factors

Often abbreviated to 'risk factors'; anything that is statistically associated with an increased chance of developing a particular disease, disorder or disability in a population; when the incidence of the disease is examined in different populations it is found to occur more frequently in those who have been exposed to the risk factor than in those who have not, or whose exposure level has been lower. (CS 1, 4, 5, 6 & 7)

disinfectant

deoxyribonucleic acid

A very long macromolecule found in the cell nucleus, abbreviated to DNA. It is the main component of chromosomes and is the material that transfers genetic characteristics through the generations in all organisms. The genetic information is carried in the sequence of the bases that make up the DNA. This sequence codes for thousands of genes that direct the manufacture of all the proteins in a cell. The form and function of proteins determines the characteristics of an individual organism. (CS 4)

DNA repair protein

Any one of numerous proteins in a mammalian cell that are part of the machinery that detects and repairs mistakes in DNA caused by errors during DNA copying, or by the effects of mutagens. They help to minimise the number of mutations, and when they are inactivated the rate of DNA mutation increases. (CS 4)

double bond

double-blind study

A study in which neither the participants (e.g. patients) nor the experimenters (e.g. therapists) know into which group the participants have been allocated (e.g. either drug or placebo groups). (CS 2)

ecotoxicology

effective dose

A measure of the dose of ionising radiation to an organism which takes into account the sensitivity to radiation of different organs in the body. Multiplied by a tissue weighting factor for that organ. Then the amounts for all the affected organs are added up to give this for the whole body. Measured in sieverts (symbol Sv). Best measure to use to estimate the likelihood of developing radiation-induced cancer. (CS 4)

elastase

electromagnetic radiation

A form of energy that can be described as either a wave or as a flow of 'packets' of energy. It includes gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves. The different types of radiation are distinguished by their wavelength and frequency; radio waves have the longest wavelength and lowest frequency; X-rays and gamma rays have short wavelengths and higher frequencies. See Book 4, Figure 4.2. (CS 4 & 7)

endothelial cells

enzyme

A protein produced by a living organism that functions as a catalyst. It facilitates other molecules entering into chemical reactions with one another, but is itself unaffected by these reactions.(CS 3, 4, 5 & 6)

epidermis

epinephrine

A hormone secreted by the suprarenal gland (formerly the adrenal gland) upon stimulation by the central nervous system in response to stress, anger, fear or exertion. It has many effects on the body, e.g. increasing heart rate and output. Also known as adrenalin. (CS 2 & 5)

epithelial cells

epithelial tissue

A tissue that covers a surface or lines a space inside the body, forming a barrier or interface across which substances are absorbed or secreted, e.g. the skin, gut lining, and various glands. (CS 4 & 6)

equivalent dose

A measure of the dose of ionising radiation to an organ that takes into account the type of radiation used. Some types of radiation are more damaging than others (because they tend to lead to double-strand breaks in the DNA rather than the more easily repaired single-strand breaks) so a radiation weighting factor is used. For X-rays this factor is 1. Measured in sieverts (symbol Sv). (CS 4)

ethanol

evolutionary trade-off

An aspect of a characteristic that represents an adaptive compromise between two opposing evolutionary pressures; e.g. the human pelvis represents a compromise between being narrow, which is necessary for running at speed, and being wide, which is necessary for giving birth to a baby with a large head. (CS 1)

excretion

expiration

extinction

A process whereby a stimulus that owes its power to conditioning loses this power by being repeatedly presented on its own; e.g. the ceasing of the capacity of a bell to trigger salivation occurs if the bell is repeatedly sounded, but without food being given. (CS 2 & 3)

fulcrum

gas pressure

The pressure exerted by a gas. It is the sum of the partial pressures of each individual gas in a mixture of gases, e.g. oxygen, carbon dioxide, nitrogen and other gases that make up the air in the lungs. (CS 5)

gas transfer test

gate theory

A theory of pain that was first proposed by Patrick Wall and Ronald Melzack in 1965. It suggests that there is, metaphorically speaking, a 'gate' within the spinal cord such that, if the gate is closed, nociceptive messages can be blocked. If the gate is open, the nociceptive signal can gain access to the brain and hence trigger pain. (CS 2)

gene

A segment of this contains the coded information required for a cell to make a particular protein. Humans probably have about 25 000. Different forms or variants of these, called alleles, determine how these characteristics are expressed in a given individual. Undergo mutation when their sequence changes. (CS 3, 4, & 5)

hepatitis

high-risk screening

A screening programme (sometimes called 'individual screening' or 'targeted screening') that identifies individuals who are likely to be at substantially greater risk of developing a certain condition than others in their population group. These individuals are sought out for regular screening, e.g. people with diabetes are screened for signs of visual impairment more often than non-diabetics. (CS 4)

hippocampus

homeostasis

A property of the body in which a number of its important parameters are held near to constant and any deviation from their normal value triggers action that tends to restore normality. It is exemplified by the maintenance of body temperature, or of oxygen concentration in the bloodstream, etc. (CS 1)

hominids

hormone

A substance produced by an endocrine gland that is carried around the body in the blood, and affects the structure or functions of specifically receptive target organs or tissues. (CS 1, 2, 3, 4, 5 & 6)

hydrogen bond

A type of chemical bond formed between a partial positive charge on a hydrogen atom and a partial negative charge on another atom. In more detail, the bond is formed by the electrical attraction occurring between the partial positive charge remaining on a hydrogen atom that is attached to an electron-attracting atom (usually oxygen or nitrogen), and the partial negative charge on the other atom in the bond (usually oxygen or nitrogen) which is attracting an electron from the hydrogen atom. Responsible for maintaining the complex three-dimensional structure of large organic molecules such as proteins and DNA. (CS 1, 3, 4 & 7)

hyperopia

hyperventilate

hypnosis

A technique in which a person is placed in a particular psychological state and, in response to suggestions made by the hypnotist, can experience alterations in perception, memory and voluntary action. (CS 2 & 6)

inflammation

inflammatory mediators

Molecules or proteins released by immune system cells in the region of an injury, infection or other damage to the tissues. They have several effects including dilation (widening) of blood vessels to increase blood supply to the region. They also attract other immune system cells. (CS 5)

information processing

inhibitory synapse

A synapse at which the release of neurotransmitter from a presynaptic neuron has an inhibitory effect on a postsynaptic cell, i.e. it inhibits the appearance of action potentials in the second cell.(CS 2 & 3)

ionic bonding

ionic compound

A substance composed of positively and negatively charged ions, held together by the electrical attraction between opposite charges. Salts such as sodium chloride (NaCl), in which the ions are organised in a regular crystal lattice, are this. (CS 1 & 3)

LASIK

legal blindness

lens

a) A transparent and flexible convex structure behind the iris that (together with the cornea) refracts light. (CS 7)
b) A transparent object, usually made of glass or plastic, that refracts light. Found in spectacles, magnifying glasses and microscopes. (CS 7)

leukocytes

levers

Rigid structures (such as bones) that can move about a fulcrum in response to forces in order to transfer force from one place to another. They can modify the size of the force and the distance of motion. (CS 6)

lobule

lock-and-key interaction

The binding that occurs between a signalling molecule and its specific receptor. The specificity of the binding is analogous to that of a particular key in a particular lock; e.g. the binding between a neurotransmitter and its receptor, or a hormone and its receptor. (CS 1, 2 & 4)

lung function test

lymph node

A bean-shaped tissue packed with immune system cells found at intervals along the vessels of the lymphatic system. They filter potentially harmful substances and organisms (microbes) from body fluids that drain into the lymphatic system; the filtered fluid (lymph) is returned to the blood stream. (CS 4)

mammography

media

Substances in which an interaction or reaction occurs, or in which an event takes place, or chemicals or objects are transported or supported, e.g. a medium through which a wave is transmitted in the refraction of light. (CS 7)

molecule

morbidity rate

The number of cases of a disease, disorder or disability in a population, relative to the total number of people at risk of developing it; usually expressed as the number of cases per 1000 (or per 10 000, or per 100 000 or per million) population. (CS 1)

morbidity

mortality

mortality data

mortality rate

The number of deaths in a population, either from all causes combined or from a specific cause, expressed as a rate per 1000 (or per 10 000, or per 100 000 or per million) people in the population. (CS 1, 4 & 6)

motor neuron

mucus

A slimy, viscous substance secreted as a protective lubricant by the cells in the lining of the nose, throat and airways. Traps microbes and particles and is swept out of the respiratory system into the throat, to be coughed out or swallowed. Also secreted by the gut where it lubricates the passage of food and protects the cells lining the gut. (CS 5)

multifactorial disease

Diseases or disorders that develop as a result of the interaction over time of a combination of different risk factors, none of which on its own would be likely to cause the disease. These may include the inheritance of certain gene mutations from a parent, exposure to chemical and biological agents from environmental sources, and individual characteristics such as age or gender or obesity. (CS 3 & 5)

mutagen

mutation

A change in the sequences of bases in the DNA of an organism, resulting in an alteration in the manufacture or function of a body protein. Also refers to the process by which such a change in DNA sequence occurs due to the action of a mutagen, e.g. radiation, or DNA-damaging chemicals in the environment. (CS 4)

myopia

natural selection

A process causing evolutionary change over time (from one generation to the next). Individuals that hold an advantage in terms of survival and reproduction, in competition with other individuals, will pass on characteristics that contribute to that advantage to successive generations, provided that those characteristics have a genetic basis. As a result, these characteristics become more common in the population over successive generations. (CS 1)

nearwork activity

negative feedback

A process whereby a parameter is maintained at a nearly constant value because deviations from its normal value tend to trigger actions that 'negate' the deviation and return it to normality; e.g. a fall in body temperature is fed back via the nervous system, which triggers shivering and this tends to raise body temperature back to normal. (CS 2)

negative predictive value

For a screening procedure such as mammography, this value is the number of true negative results expressed as a percentage of the total number of negative results (true or false). It tells (other things being equal) what the chance is that a person with a negative test result actually does not have the disease being screened for. (CS 4)

neuron

neurotransmitter

A chemical that is stored within the axon terminal of a neuron and is released in response to electrical activity within that neuron. It passes the short distance to a neighbouring cell (neuron or muscle cell) where it binds to a neurotransmitter receptor, initiating an effect in that cell. The term 'synapse' describes the location of these events. (CS 2, 3, 6 & 7)

nociceptive pain

non-communicable diseases

Diseases that cannot be transmitted from person to person (also known as 'non-infectious diseases' or 'chronic conditions' or 'long-term conditions'); they mainly develop slowly over time and persist for a long period, or are irreversible; e.g. cancers, heart disease, respiratory diseases, diabetes, cirrhosis of the liver, and neuropsychiatric conditions such as Alzheimer's disease and other dementias. (CS 1)

noxious stimuli

nucleus

a) Contains protons, each of which carry a single positive electric charge, and neutrons which are uncharged. (CS 2 & 4)
b) An organelle containing the genetic material, found in most animal and plant cells. (CS 2, 4 & 6)

obesity

A condition in which a person exceeds a certain threshold for the proportion of body weight that consists of fat. In most assessments based on body mass index, a BMI of greater than 30 is defined as clinically obese. (CS 1)

oestrogens

A group of steroid hormones produced mainly by the ovaries (some are also produced by fat deposits in the body), which are responsible for promoting the development and maintenance of female sexual characteristics. (CS 4)

open angle glaucoma

The most common type of glaucoma, caused by a partial blockage of trabeculae, which reduces the rate at which the aqueous fluid can drain away from the eye and thus leads to a build up of intraocular pressure. (CS 7)

ophthalmologist

opiates

A class of substances arising from outside the body, but which bear a close similarity to naturally occurring opioids in their structure and effect; they include heroin derived from the opium poppy and morphine. (CS 2)

opportunistic screening

optical power

A measure of the refracting power of a lens. Calculated as: 1 / focal length of the lens (in metres). The unit used is dioptres (symbol D). The power of a convex lens is positive; for a concave lens it is negative. (CS 7)

pain matrix

pain

An unpleasant sensory and emotional experience traditionally associated with actual or potential tissue damage and which normally is felt to arise in a particular location in the body. The term can also be used to refer to experiences triggered by social loss. (CS 2)

physiology

placebo effect

A beneficial effect deriving from a procedure with no intrinsic benefit. It relies upon the context in which the intervention is made; e.g. a sugar pill might serve as a placebo if the patient believes that it will bring some benefits. (CS 2 & 3)

plasticity

A term that refers to the fact that the connections between neurons are not static. Rather, they are subject to change as result of activity within the neurons concerned. It can mean, over a period of time, increased sensitivity of connections between neurons in the circuits that give rise to pain and hence increasing levels of pain. (CS 2)

PM10

point-of-use' strategy

A method of purifying water, e.g. filtering, that involves individual people treating water as they use it, rather than having purified water delivered to them from a remote water-treatment plant in pipes. (CS 1)

population age-structures

population screening

A screening programme (sometimes called 'mass screening') that aims to screen everyone in a particular population group (rarely every citizen), e.g. everyone over the age of 50 years, or all newborn babies. Attempts are made to screen everyone in that category, sometimes at regular intervals. (CS 4)

positive predictive value

For a screening procedure such as mammography, the number of true positive results expressed as a percentage of the total number of positive results (true or false). It tells (other things being equal) what the chance is that a person with a positive test result actually has the disease being screened for. (CS 4)

postsynaptic neuron

post-traumatic stress disorder

A condition that may develop following exposure to an extremely stressful situation, typically where a person witnesses the violent death of someone else, or believes their own life is in danger. Symptoms include disordered sleeping, a dread of situations that remind of the original event and the experiencing of flashbacks, in which the distressing scenes are remembered as if really happening again. To be classed as PTSD these symptoms must be present more than a month after the precipitating event. (CS 6)

powers of ten

prefrontal cortex

A region of cortex at the front of the brain, where the activity of neurons is associated with voluntary control of behaviour (self-control) and restraint. Biological evidence suggests that mild to moderate doses of alcohol selectively depress the activity of neurons in the PFC, relative to other brain regions. (CS 3)

prevalence

primates

A group of mammals including monkeys, apes and humans, with limbs adapted for climbing, leaping and swinging, reflecting their arboreal (tree-living) habits or origins, and characterised by having large brains in relation to body size, a short snout and large eyes that point forwards, providing stereoscopic vision. (CS 1)

principal focal point

priority eye diseases

Leading global causes of visual impairment that have been identified by the WHO's Vision 2020 project as targets that can be prevented or treated. They include refractive errors and low vision, cataract, glaucoma, AMD, diabetic retinopathy and trachoma. (CS 7)

proportional mortality

proteins

Long chain-like molecules (polymers) made from smaller molecules called amino acids joined by chemical bonds. The chains fold up into complex shapes giving them a wide range of functions. Major constituent of all organisms. (CS 1, 2, 3, 4, 5, 6 & 7)

protons

proxy measure

A readily measured statistic or parameter that can be used in place of a more complex statistic, or to 'stand in for' one that is impossible to measure directly; e.g. disease statistics are often used as this for the 'health' of a population; the number of prescriptions for antidepressants can be used as this for the number of people with depression in a population. (CS 1 & 2)

psychobiological approach

An approach to explanation which implies two closely related things: (i) both biological and psychological sciences have central roles in the explanation, and (ii) a given phenomenon to be studied within this perspective, such as pain, has both biological and psychological aspects. (CS 2 & 3)

psychological trauma

pulmonary hypertension

pulmonary rehabilitation

A multi-disciplinary programme of care for patients with chronic respiratory conditions, which is tailored to the individual and combines exercise and education to address all aspects of living with the condition.(CS 5)

pyloric sphincter

radiographer

Qualified to employ a range of equipment such as X-rays, MRI scanners, etc. to produce images to diagnose an injury or disease. They will then have undergone further specialist training in mammography. (Two types, diagnostic and therapeutic; the latter have undergone training to enable them to operate radiotherapy machines that treat cancer and to calculate (or plan) the arrangement of X-ray beams for the treatment.) (CS 4)

radiologist

receptor

A complex specialised molecule embedded in the outer membrane of a cell, or in its internal structure, which has a unique three-dimensional shape and patterns of electrical charge that enable it to bind specifically to a particular signalling molecule (e.g. a hormone or neurotransmitter). (CS 1, 2, 3, 4, 5 & 6)

reinforcer

relative risk

An estimate of the probability of developing a particular disease or disorder in a population that has been exposed to a particular risk factor, relative to the probability of developing the condition if the risk factor was not present. (CS 4)

residual volume

respiration

The total process in an organism by which oxygen is conveyed to tissues and cells, oxidation of nutrient molecules releases useable energy, and the oxidation products (carbon dioxide and water) are given off. (CS 5)

respiratory centres

The areas of the medulla region in the brain that integrate sensory information from chemoreceptors monitoring the level of oxygen and carbon dioxide in the blood. They send out appropriate signals to regulate the rate of contraction of the respiratory muscles (including the diaphragm and rib muscles). (CS 5)

respiratory system

The system of organs and structures in which gas exchange takes place. In mammals it consists of the airways, the lungs and the muscles that mediate the movement of air into and out of the lungs. (CS 5)

retina

reward

An event that follows a particular behaviour and which strengthens the tendency to repeat that behaviour. For example, if relaxation follows drinking alcohol it would be said to reinforce the tendency to drink alcohol. (CS 3)

risk factor

Anything that is statistically associated with an increased chance of developing a particular disease, disorder or disability in a population; when the incidence of the disease is examined in different populations it is found to occur more frequently in those who have been exposed to this than in those who have not, or whose exposure level has been lower. (CS 1, 4, 5, 6 & 7)

scar

scatter plot

A graphical method of showing whether two numerical variables are related to one another. They are called 'variables' because they can each have a range of possible values. Each data point represents a particular entity, such as a country, for which the two variables have been measured. (CS 1)

Schwann cells

screening

The systematic application of a test or investigation to people who have not sought medical attention, in order to identify those whose risk of developing a particular disease is sufficient to justify further action. (CS 4)

selection pressure

The environmental factors impacting on survival and reproduction in a population of organisms in which there is variation between individuals in their ability to withstand adverse conditions or benefit from advantageous circumstances. The result of this (e.g. exposure to antibiotics in bacterial populations) is that individuals who are best adapted to withstand it or benefit from it leave a larger proportion of offspring in the next generation, while those who are less well adapted suffer reproductive disadvantage. (CS 1)

skeletal muscle

Snellen letter chart

The eye chart used to determine how well a person can see at various distances. Named after a 19th-century Dutch ophthalmologist Hermann Snellen (1834-1908) who devised a test for visual acuity. (CS 7)

somatic nervous system

specificity

A screening procedure has high of this if, in people who do not have the disease being screened for, the procedure is very likely not to detect disease, that is, to give a negative result. Numerically, this is calculated by expressing the number of true negative results as a percentage of the total number of people (true negatives + false positives) that actually do not have the disease. (CS 4)

stem cells

stochastic

This refers to a random effect of ionising radiation. There is no radiation threshold at which the effect inevitably occurs, but the probability of an effect occurring increases with the amount of radiation received. (CS 4)

stress response

stress

The experience of being in an unpleasant situation, over a period of days, weeks or longer, in which one is unable to exert control over circumstances which are not of one's choosing. The coping resources necessary to meet the demands of this unpleasant situation are lacking. (CS 1)

stunting

subjective experience

An experience which is accessible only to the person who experiences it in terms of the contents of his or her conscious mind. Such experience is not open to objective observation or measurement by any other individual and hence is contrasted with 'objective experience'. (CS 2)

wavelength

wave-particle duality

The behaviour of electromagnetic radiation cannot be adequately described in all situations by any one model. In some situations the wave model is appropriate, in others the particle model, which describes the radiation as photons, must be used. (CS 4 & 7)

wet AMD

A type of age-related macular degeneration (AMD) in which new blood vessels form in an attempt to restore the blood supply to the retina. The new vessels are fragile, and may leak blood into the eye. (CS 7)

wind-up

A form of plasticity within the connections between the neurons that underlie nociception and pain, such that, over time, increasing levels of pain are experienced even though the stimulus remains unchanged. (CS 2)

withdrawal symptoms

Characteristic signs that follow the termination of taking a drug, most usually associated with a negative mood. There can also be characteristic physiological signs associated with particular drugs, e.g. sweating and shivering. (CS 3)

xenobiotic

vasopressin

A hormone which is normally secreted by the brain in response to decreased water levels in the body. When alcohol is drunk, ethanol acts on the brain and inhibites the release of this, allowing the kidneys to make more urine.